Neuroblastoma is the most common extracranial solid tumor in infants and children, and accounts for more than 15% of cancer-related deaths in children. Despite recent advances in combined modality treat- ment, the overall mortality for all stages of tumors remains significant at 50%. As a neuroendocrine tumor, neuroblastomas can produce various gastrointestinal (GI) hormones and the amount of peptide expression has been associated with the clinical tumor behavior suggesting a potential role for gut )eptides as autocrine growth factors. Gastrin-releasing peptide (GRP) is a gut/neuropeptide that stim- Jlates the growth of normal and neoplastic tissues and has also been found to be an autocrine growth factor for some cancers. Our studies have identified an increased expression of GRP-receptors (GRP-R) in more aggressive undifferentiated neuroblastomas. Additionally, we have found that GRP functionally couples to GRP-R to stimulate tumor growth, suggesting a role of GRP as an autocrine growth factor for neuroblastomas. Furthermore, we have demonstrated that phosphatidylinositol 3-kinase (PI3-K) pathway, an important signal transduction pathway involved in cell survival, regulates GRP-R expression in neuroblastoma. Based on our findings, the central hypothesis of this proposal is that GRP stimulates the growth of neuroblastoma cells through the activation of GRP-R, which in turn is regulated by PI3-K signal transduction pathway. To examine this, we have planned the following Specific Aims: 1) to further characterize the expression of GRP-R and its ligand GRP in human neuroblastomas, 2) to delineate the molecular mechanisms regulating GRP-R expression in neuroblastomas, 3) to determine the effects of the GRP/GRP-R pathway on neuroblastoma growth. Understanding the factors regulating GRP/GRP-R expression will provide novel and important information regarding the potential rote of GRP as an autocrine growth factor for neuroblastomas. This information is clinically significant because either expression of GRP-R or GRP may act as a tumor marker to predict tumor aggressiveness or potential response to therapy. Furthermore, a better understanding of the cellular mechanisms and signaling pathways regulating neuroblastoma cell growth could potentially lead to the development of novel therapeutic aqents as adjuvant treatment for this devastating disease.